首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   17340篇
  免费   2610篇
  国内免费   2148篇
化学   13289篇
晶体学   277篇
力学   937篇
综合类   187篇
数学   1717篇
物理学   5691篇
  2024年   24篇
  2023年   251篇
  2022年   441篇
  2021年   526篇
  2020年   605篇
  2019年   616篇
  2018年   470篇
  2017年   483篇
  2016年   780篇
  2015年   753篇
  2014年   912篇
  2013年   1258篇
  2012年   1521篇
  2011年   1601篇
  2010年   1146篇
  2009年   993篇
  2008年   1146篇
  2007年   969篇
  2006年   969篇
  2005年   922篇
  2004年   732篇
  2003年   646篇
  2002年   719篇
  2001年   480篇
  2000年   434篇
  1999年   384篇
  1998年   285篇
  1997年   262篇
  1996年   253篇
  1995年   236篇
  1994年   188篇
  1993年   172篇
  1992年   160篇
  1991年   137篇
  1990年   123篇
  1989年   99篇
  1988年   86篇
  1987年   57篇
  1986年   61篇
  1985年   63篇
  1984年   33篇
  1983年   29篇
  1982年   21篇
  1981年   20篇
  1980年   9篇
  1979年   7篇
  1974年   2篇
  1971年   2篇
  1957年   6篇
  1936年   1篇
排序方式: 共有10000条查询结果,搜索用时 818 毫秒
781.
782.
783.
784.
Based on quantum chemistry calculations combined with the Marcus–Hush electron transfer theory, we investigated the charge‐transport properties of oligothiophenes (nTs) and oligopyrroles (nPs) (n=6, 7, 8) as potential p‐ or n‐type organic semiconductor materials. The results of our calculations indicate that 1) the nPs show intrinsic hole mobilities as high as or even higher than those of nTs, and 2) the vertical ionization potentials (VIPs) of the nPs are about 0.6–0.7 eV smaller than the corresponding VIPs of the nTs. Based on their charge‐transport ability and hole‐injection efficiency, the nPs have potential as p‐type organic semiconducting materials. Furthermore, it was also found that the maximum values of the electron‐transfer mobility for the nTs are larger by one‐to‐two orders of magnitude than the corresponding maximum values of hole‐transfer mobility, which suggests that the nTs have the potential to be developed as promising n‐type organic semiconducting materials owing to their electron mobility.  相似文献   
785.
Hierarchical flower-like architectures of[Ni3(BTC)2·12H2O](BTC3=benzene-1,3,5-tricarboxylate) were successfully prepared by a simple solution-phase method under mild conditions without any template or surfactant.Phase-pure porous NiO nanocrystals were obtained by annealing the Ni-BTC complex without significant alteration in morphology.The product was characterized by X-ray diffraction techniques,field-emission scanning electron microscopy(FESEM).transmission electron microscopy(TEM) and high-resolution TEM(HRTEM).The catalytic effect of the NiO product was investigated on the thermal decomposition of ammonium perchlorate(AP) and it was found that the annealed NiO product has higher catalytic activity than the commercial NiO.  相似文献   
786.
In this paper,we developed and validated a simple,sensitive,and selective high-performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS) method to identify and measure the following prohibited substances that may be found in cosmetic products:minoxidil,hydrocortisone, spironolactone,estrone,canrenone,triamcinolone acetonide and progesterone.Chromatographic separation was performed on a Waters Symmetry C18(100 mm×2.1 mm,3.5μm particle size) with a gradient elution system composed of 0.2%(v/v) formic acid aqueous solution and methanol containing 0.2%(v/v) formic acid at a flow rate of 0.3 mL/min.The substances were detected using a triple quadrupole mass spectrometer in the multiple reaction monitoring mode with an electrospray ionization source.All of the calibration curves showed good linearity(r > 0.999) within the tested concentration ranges.The limit of detection was <25 pg.The relative standard deviations for intraday precision for each of the prohibited substances were <3.5%at two concentration levels(2μg/g,10μg/g). The relative recovery rate for each of the prohibited substances ranged from 91.8%to 111%at three concentration levels(0.1μg/g,2μg/g,10μg/g),including the limit of quantification.In conclusion,we have developed and validated a method that can identify seven prohibited substances in cosmetic products.  相似文献   
787.
A series of triazole and benzotriazole derivatives as novel p90 ribosomal S6 protein kinase 2 (RSK2) inhibitors were designed and synthesized. The in vitro activities against RSK2 were evaluated, and among 14 compounds, compounds 5, 6, 11, 12, 13 and 14 exhibited enzyme IC50 values of 8.91, 2.86, 3.19, 3.05, 4.49 and 2.09 μmol/L re- spectively. The proposed binding modes were simulated using molecular docking method, and the docking results coupled with the stmcture-activi1:y relationship (SAR) analysis indicated that all these active compounds bound to the RSK2 ATP binding site at NTKD, and the electron-donating groups on the 4-position of phenyl were the deter- minant point for the inhibitory activity.  相似文献   
788.
配体[C5Me4HR][R=4-BrPh(1),(MeC5H3N)CH2(2)]分别与Mo(CO)6,Ru3(CO)12和Fe(CO)5在二甲苯中加热回流,得到了6个双核配合物trans-[η5-C5Me4R]2Mo2(CO)6(3,4),trans-[(η5-C5Me4R)Ru(CO)(μ-CO)]2(5,6)和trans-[η5-(C5Me4R)Fe(CO)(μ-CO)]2(7,8,).通过元素分析、红外光谱、核磁共振氢谱对配合物的结构进行了表征,并用X-射线单晶衍射法测定了配合物3,5,68的结构.  相似文献   
789.
建立超高效液相色谱–串联质谱法鉴别十字花科植物中硫代葡萄糖苷的分析方法。采用70%甲醇水溶液提取白芥种子中的硫代葡萄糖苷,通过反相C18柱分离,电喷雾–离子阱–飞行时间质谱测定。利用硫代葡萄糖苷二级质谱裂解产生的m/z 195,241,259,275,291特征离子和伴随产生的80,162,163,196,242 Da中性分子丢失规律,共鉴别出5种硫代葡萄糖苷。  相似文献   
790.
The electrochemical behavior of dopamine (DA) at a MWNTs-modified glassy carbon electrode was investigated by cyclic voltammetry (CV), square wave voltammetry (SWV). The MWNTs modified electrode exhibited marked promotion of the electrochemical reaction of DA in different environments. Under optimum conditions, the peak currents of SWV of DA were increased linearly with incremental concentration of DA in the range from 5 × 10?7 to 1 × 10?5 mol L?1. The limit of detection is 3 × 10?7 mol L?1.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号